jn190068@longs.LANCE.ColoState.EDU (Jay Lewis Nestle) (09/25/90)
I was working on a simple heat transfer problem and was
using my 48SX. I was using C degrees, my answers seemed to be
enter 1 degree C twice then add them, the answer
is: 275.15 degrees C
This is clearly wrong: Either 275.15 K or 2 deg C
would be great, but it seems that the 48 is forgetting
to convert back to deg C but is informing the user
that it has. Bug!!!
Are there any more of these LITTLE problems that a
user should know about. Do the rest of the unit conversion
routines work fine??? Is it fixed in E?
Thanks, Jay Nestle
jn190068@longs.lance.colostate.edu
...ncar!boulder!ccncsu!longs.lance.colostate.edu!jn190068
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| |jurjen@cwi.nl (Jurjen NE Bos) (09/25/90)
jn190068@longs.LANCE.ColoState.EDU (Jay Lewis Nestle) writes: > > I was working on a simple heat transfer problem and was >using my 48SX. I was using C degrees, my answers seemed to be > enter 1 degree C twice then add them, the answer > is: 275.15 degrees C > This is clearly wrong: Either 275.15 K or 2 deg C Think about it. What does adding temperatures mean, anyway? For example, how much is 35,6 degrees F + 35,6 degrees F? a) 71.2 degrees F (because that's "logical") b) 39.2 degrees F (because 39.2 is 2 degrees C, and 4 degrees C is 39.2 F) c) 530.87 degrees F It is clear that the answer must be c) There is only ONE way to add temperatures: add the distances from the absolute zero. So the 48 was right, after all. -- | | "Never imagine yourself not to be otherwise than what | | Jurjen N.E. Bos | it might appear to others that what you were or might | | | have been was not otherwise than what you had been | | jurjen@cwi.nl | would have appeared to them to be otherwise." |
bson@rice-chex.ai.mit.edu (Jan Brittenson) (09/26/90)
In article <9682@ccncsu.ColoState.EDU> jn190068@longs.LANCE.ColoState.EDU (Jay Lewis Nestle) writes: > I was working on a simple heat transfer problem and was >using my 48SX. I was using C degrees, my answers seemed to be > > enter 1 degree C twice then add them, the answer > is: 275.15 degrees C If you do 1_K 1_C + you get 2_C. If you do 1_C 1_K + you get 275.15_K. Same goes for F, but difference values. Assume we're adding 0C and 0C. What are we trying to accomplish? Adding two freezing points? Doesn't make sense. You can add Kelvin and Kelvin, and get Kelvin since it's an SI unit, but not C + C. It won't make sense. You can add 1 to 1C and get 2C. What is the unit-less 1 then? Well, it's one C _scale unit_, i.e. 1K. Remember that 0C is 273.15K. If you add 0C to 0C, you'll have 2*273.15K. To convert the answer back, subtract 273.15K, and you're still left with 273.15C. So I'm afraid the 48 is doing the right thing here. (Which presumably, is what you wanted like to hear, after all. :-))
edp@jareth.enet.dec.com (Eric Postpischil (Always mount a scratch monkey.)) (09/26/90)
In article <9682@ccncsu.ColoState.EDU>, jn190068@longs.LANCE.ColoState.EDU (Jay Lewis Nestle) writes: > enter 1 degree C twice then add them, the answer > is: 275.15 degrees C > > This is clearly wrong: Either 275.15 K or 2 deg C > would be great, but it seems that the 48 is forgetting > to convert back to deg C but is informing the user > that it has. Bug!!! This isn't wrong or a bug. It is described in the manual. See "Adding and Subtracting Temperature Units" on page 201. The Celsius and Farenheit scales are not zero-based. That is, 0 degrees C and 0 degrees F are not really zero anything; they are just a position on the scale. Whenever you add pure temperatures, the calculator adds absolute temperatures. It's equivalent to converting to kelvins, take the two numbers of kelvins, adding the numbers, interpreting the sum as a number of kelvins, and converting back to whatever scale. If a unit contains a temperature but also contains other units (or contains only temperature but with some exponent), the calculator will treat the temperature as a relative temperature -- that is, as an indication of the difference of two temperatures, rather than an absolute temperature. To add x degrees C and y degrees C, you could add them and subtract 0 degrees C or you could multiply them by some other unit, perform the addition, and divide by the other unit. (The second method works whether the inputs are Farenheit, Celsius, or whatever. The first requires you to know the scale.) -- edp
kaufman@delta.eecs.nwu.edu (Michael L. Kaufman) (09/26/90)
In article <9682@ccncsu.ColoState.EDU> jn190068@longs.LANCE.ColoState.EDU (Jay Lewis Nestle) writes: > enter 1 degree C twice then add them, the answer > is: 275.15 degrees C > > This is clearly wrong: Either 275.15 K or 2 deg C > would be great, but it seems that the 48 is forgetting > to convert back to deg C but is informing the user > that it has. Bug!!! This has been discussed before. Here is the problem: 1_c is not one degree of c. It is instead 1 on the c scale which goes from -274 up. All of the additions on the 48 use absolute zero as a base. what is needed is the units "degrees of c" to go along with "c degrees" barring this, just remember to convert to K before you do any additions. This is annoying, but it is not a bug. Michael =============================================================================== Michael L. Kaufman \\ "His imagination resembled the wings of an Ostrich. It kaufman@eecs.nwu.edu \\ enabled him to run, though not to soar." T. Macaulay ===============================================================================